High torque capacity wet paper friction member

ABSTRACT

[Problems]To provide a wet paper friction member which has high torque capacity and excellent thermal stability simultaneously.  
     [Solution Means]A wet paper friction member is produced by impregnating thermosetting resin into a paper body; curing it with heat; and then forming it with pressure. A fiber base material comprises 20-80 wt % of the paper body and comprises cellulose pulp, aramid pulp, and homopolymer acrylic pulp the drainability of which is adjusted to 120-280 ml, and thermosetting resin such as straight phenol resin, alkyl modified phenol resin, epoxy modified phenol resin, tung oil modified phenol resin, cashew oil modified phenol resin, tung oil/cashew modified phenol resin is impregnated at 20-40 wt %, and thereby, high torque capacity and heat resistance, and mechanical strength are realized simultaneously.

DETAILED DESCRIPTION OF THE INVENTION

1. Technical Field to Which the Invention Belongs

The present invention relates to a wet or wet-tpype paper frictionmember used in a clutch and brake component of an automatic transmissionof a vehicle.

2. Prior Art

A wet paper friction member is produced by dispersing a mixture of afiber base material such as pulp and a friction modifier in water andforming a paper body; making it dry and thereafter, impregnating it withthermosetting resin; heating and curing it; and then forming it withpressure. The functions of a wet paper friction member are influenced bya blend of the fiber base material, a filler and the friction modifieretc. which are main components of the paper body, and impregnatedthermosetting resin. Therefore, choice and blending amount of materialshave been researched for improvement of a wet paper friction memberaccording to its use.

It has been known that a friction modifier has an important role ininfluencing porosity and surface configuration of a friction member; andfiber ingredient affects porosity and flexibility of the friction memberand thus, has an influence on friction property and heat resistance, andmechanical strength.

Phenol resin which is used mainly as a binder has an influence not onlyon mechanical strength of a friction member but also on frictionalcoefficient as well as velocity dependence of the frictionalcoefficient. Particularly, since frictional coefficient in the lowvelocity range which is referred to as ‘torque capacity’ is highlyinfluenced by resin, the research has been made using various oil-basedmaterials or modified materials.

For example, Patent Document 1 discloses a wet paper friction memberwhich is produced by blending pulp which is fibrillatedpoly-acrylonitrile-based copolymer acrylic fiber (hereinafter referredto as the ‘copolymer acrylic pulp’) and filler, and thus, forming apaper body; and impregnating it with thermosetting resin and then curingit.

[Patent Document 1]

Japanese Patent Publication No. 45808/1993

PROBLEMS TO BE SOLVED BY THE INVENTION

In a clutch and brake component of an automatic transmission, theability to transmit torque in the state where it is stopped or slightlyslides is the most fundamental function and referred to as the torquecapacity. If torque capacity is high, for example, a diameter of aclutch can be reduced or the number of friction members can be reducedand thus, a clutch component can be miniaturized. On the other hand,calorific value per unit area of a brake and a clutch during operationincreases due to high frictional coefficient. This tends to lower theheat resistance and mechanical strength of the friction member; andtherefore, a wet paper friction member which is excellent in torquecapacity, heat resistance and mechanical strength could not be easilyproduced.

As for the wet paper friction member of Patent Document 1, copolymeracrylic pulp is particularly low in heat resistance and chemicalresistance, and therefore, contraction of dimension is caused duringprocessing step of a wet paper friction member. Therefore, accurateprocessing has been difficult, or there have been other problems suchthat large strength degradation of the friction member is occurredduring operation due to frictional heat or chemicals in automatictransmission fluid.

In view of the above problems, it is an object of the present inventionto provide a wet paper friction member which is used mainly in a clutchand a brake of an automatic transmission and has high torque capacityand excellent thermal stability simultaneously. Improvement was made byfocusing attention on a fiber base material and resin in a frictionmodifier forming a paper body among compositions of a conventional wetpaper friction member. This realized successful development of a hightorque capacity wet paper friction member which has friction property,heat resistance and mechanical strength simultaneously, and has highversatility without limitation to its application.

MEANS TO SOLVE THE PROBLEM

The present invention solved the above-mentioned problems by providing awet paper friction member which is produced by impregnatingthermosetting resin into a paper body, curing it by heat, and forming itwith pressure, wherein said paper body comprises fiber base material andfiller, characterized in that said fiber base material comprises 20-80wt % of the total weight of said paper body, and comprises cellulosepulp, aramid pulp, and homopolymer acrylic pulp the drainability ofwhich is 120-280 ml.

[Function]

The present invention can provide a wet paper friction member havingexcellence in torque capacity, heat resistance and mechanical strengthsince the fiber base material comprises 20-80 wt % of the total weightof the paper body, and comprises cellulose pulp, aramid pulp, andhomopolymer acrylic pulp the drainability of which is 120-280 ml.

[Embodiments]

A wet paper friction member according to the present invention isproduced by blending specified fiber base material and filler etc. andthus, producing a paper body; impregnating the paper body withthermosetting resin; curing it by heating; and forming it with pressure.The fiber base material comprises cellulose pulp, aramid pulp,homopolymer acrylic pulp and other fibers at 20-80 wt % of the totalweight of the paper body. Drainability of the homopolymer acrylic pulpis adjusted to 120-280 ml. Thermosetting resin such as straight phenolresin, alkyl modified phenol resin, epoxy modified phenol resin, tungoil modified phenol resin, cashew oil modified phenol resin and tungoil/cashew oil modified phenol resin is impregnated into said paper bodyat 20-40 wt %. Thus, high torque capacity, heat resistance andmechanical strength are realized simultaneously.

The fiber base material comprises cellulose pulp, aramid pulp,homopolymer acrylic pulp and other fiber at 20-80 wt % of the totalweight of the paper body.

While aramid pulp has excellent thermal stability and paper-makingproperty, it is expensive in comparison with cellulose pulp, and alsohas inferior compatibility with thermosetting resin such as phenolresin. In addition, while cellulose pulp has better compatibility withresin and is cheaper in comparison with aramid pulp, it is inferior inthermal stability and mechanical strength. On the other hand,homopolymer acrylic pulp has excellent compatibility with thermosettingresin such as phenol resin and has a characteristic that it does notthermofuse. Therefore, when it is used with aramid pulp and cellulosepulp, excellent thermal stability and mechanical strength can beachieved at low cost. When the amount of the fiber base material isabove 80 wt % of the total weight of the paper body, smooth membersurface can not be obtained. When it is below 20 wt %, mechanicalstrength is lowered.

Drainability of homopolymer acrylic pulp forming a paper body isadjusted to 120-280 ml.

Drainability is a degree of beating of fiber, and the smallerdrainability is, the larger the degree of beating of fiber is, resultingin increase of splitting degree of each fiber. When splitting degree ofacrylic pulp is increased, intertwist between fibers increases, andsufficient mechanical strength can be obtained after phenol resin isimpregnated and cured.

When homopolymer acrylic pulp the drainability of which is smaller than120 ml is used for the one forming a paper body, the amount of splitfiber is too large and the size of holes becomes too small, andtherefore, clogging tends to be caused during frictional sliding, andheat resistance is lowered.

When aramid pulp the drainability of which is above 280 ml is used forthe one forming a paper body, intertwist between fibers becomes smalland therefore, sufficient mechanical strength can not be obtained.

As thermosetting resin, any one or some of resins among straight phenolresin, alkyl modified phenol resin, epoxy modified phenol resin, tungoil modified phenol resin, cashew oil modified phenol resin and tungoil/cashew oil modified phenol resin can be used to be impregnated intosaid paper body at 20-40 wt %.

In general, tung oil modified phenol resin, cashew oil modified phenolresin and tung oil/cashew oil modified phenol resin etc. are known to beeffective in increasing frictional coefficient in the low velocityrange. On the other hand, when such oil modified materials are used,there are problems such that heat resistance and mechanical strength arelowered. In the meantime, straight phenol is not so effective inincreasing frictional coefficient in the low velocity range, but, it hassufficient heat resistance and mechanical strength. Therefore, when itis used with the above-mentioned modified materials, high frictionalcoefficient and heat resistance, as well as mechanical strength can beachieved simultaneously. When the amount of these resins impregnatedwith a paper body was under 20 wt % of the total weight of the frictionmember, sufficient mechanical strength can not be obtained, and when itis 40 wt % or more, heat resistance is lowered.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] A graph showing the results of torque capacity evaluation;

[FIG. 2] A graph showing the results of durability evaluation;

[FIG. 3] A graph showing the results of durability evaluation; and

[FIG. 4] A graph showing the results of compressive strength evaluation.

EXAMPLES

Examples will be explained concretely below.

Example

A clutch disk was produced by impregnating oil modified straight phenolresin into a paper body comprising 10 wt % of cellulose pulp, 10 wt % ofaramid pulp, 30 wt % of homopolymer acrylic pulp, and 50% of filler suchas diatomaceous earth, at 30 wt % of a friction member; curing it byheating, and then bonding it to a core plate.

Comparative Example

As Comparative Example, a clutch disk was produced by impregnatingstraight phenol resin into a paper body comprising 30 wt % of cellulosepulp, 30 wt % of aramid pulp, 30 wt % of diatomaceous earth, and 10 wt %of carbon-based filler, at 35 wt % of a friction member; curing it byheating; and then bonding it to a core plate.

Torque capacity, heat resistance and mechanical strength of a wetfriction clutch disc produced by the above-mentioned processes wereevaluated by the following testing methods:

<Conditions for Torque Capacity Evaluation>

-   Testing device: SAE No. 2 friction testing apparatus-   Condition for achieving performance: number of friction surfaces: 6-   Oil temperature: 80 degrees Celsius-   Surface pressure: 0.5 MPa, 1.0 MPa, 2.0 MPa-   Rotational speed: 0.72, 1, 5, 10, 25, 50, 75, 100 rpm

As a result of the above tests, a wet paper friction member of Examplehad high frictional coefficient at low speed, that is, high torquecapacity, and also had excellent velocity property of the frictionalcoefficient.

<Condition for High-Speed Durability Evaluation>

-   Testing device: SAE No. 2 friction testing apparatus-   Condition for achieving performance: number of friction surfaces: 6-   Oil temperature: 100 degrees Celsius-   Surface pressure: 0.785 MPa-   Rotational speed: 7100 rpm-   Inertial mass: 0.01 Kg·m/s²-   Amount of lubricating oil: 360 ml/min

As a result of the above tests, a wet paper friction member of Examplehad small deterioration of frictional coefficient, that is, high heatresistance, and also had relatively small abrasion loss after the testin comparison with Comparative Example as shown in FIGS. 2 and 3.

<Condition for Compressive Strength Evaluation>

-   Testing device: repetitive compressive strength testing apparatus-   Condition for evaluation: number of friction surfaces: 2-   Oil temperature: 120 degrees Celsius-   Surface pressure: 10.0 MPa-   Cycle: loading 2 sec, unloading 4 sec

As a result of the above tests, a wet paper friction member of Examplehad relatively excellent mechanical strength in comparison withComparative Example as shown in FIG. 4.

It is known from FIGS. 1-4 that a friction member of Example had hightorque capacity along with sufficient heat resistance and mechanicalstrength in comparison with a friction member of Comparative Example

It is known from the above results that when a fiber base body comprisescellulose pulp, aramid pulp, homopolymer acrylic pulp and other fibersat 20-80 wt % of the total weight of a paper body; drainability ofhomopolymer acrylic pulp is adjusted to 120-280 ml; and moreover,thermosetting resin such as straight phenol resin, alkyl modified phenolresin, epoxy modified phenol resin, tung oil modified phenol resin,cashew oil modified phenol resin, tung oil/cashew oil modified phenolresin, is impregnated into said papermaking body at 20-40 wt % of afriction member, high torque capacity, heat resistance and mechanicalstrength are achieved simultaneously. This high torque wet paperfriction member can be used for many wet friction applications.

ADVANTAGES OF THE INVENTION

According to the present invention, a fiber base material comprises20-80 wt % of the total weight of a papermaking body, and comprisescellulose pulp, aramid pulp, and homopolymer acrylic pulp thedrainability of which is 120-280 ml, and thereby, the effects ofimproving torque capacity, heat resistance and mechanical strength of awet paper friction member are achieved.

1. A wet paper friction member which is produced by impregnatingthermosetting resin into a paper body; curing it by heating; and formingit with pressure, wherein said paper body comprises fiber base materialand filler, characterized in that said fiber base material comprises20-80 wt % of said paper body and comprises cellulose pulp, aramid pulp,and homopolymer acrylic pulp the drainability of which is 120-280 ml. 2.A wet paper friction member as claimed in claim 1, wherein saidthermosetting resin comprises any one of some of resins among straightphenol resin, alkyl modified phenol resin, epoxy modified phenol resin,tung oil modified phenol resin, cashew oil modified phenol resin, tungoil/cashew oil modified phenol resin.
 3. Cancelled
 4. A wet paperfriction member as claimed in claim 1, wherein said thermosetting resincomprises 20-40 wt % of said friction member.
 5. A wet paper frictionmember as claimed in claim 2, wherein said thermosetting resin comprises20-40 wt % of said friction member.